Highlights

Charge transport plays a pivotal role in a multitude of scientific and industrial applications. At room temperature and above, this charge transport is primarily influenced by the thermal vibrations of atoms within the material. Traditional computational approaches have relied on many-body perturbation theory (MBPT) and the Boltzmann transport equation (BTE), which approximate atomic vibrations as simple harmonic motions. However, these approximations often fall short when dealing with strongly anharmonic materials or high-temperature conditions, where atomic vibrations become more complex and irregular.

To address these limitations, researchers from the NOMAD laboratory at the Fritz Haber Institute have developed a novel non-perturbative approach that combines ab initio molecular dynamics (aiMD) with the Kubo-Greenwood (KG) formula. "Unlike perturbative descriptions, this approach captures all orders of anharmonic and electron-vibrational couplings," explains Jingkai Quan, the publication’s first author. The team implemented several numerical strategies to overcome the traditionally slow convergence of the KG formalism, making their calculations both efficient and accurate. Their method has been integrated into the all-electron code FHI-aims, and an accompanying tutorial showcases its usage.

The power of this new approach becomes evident in its application to strongly anharmonic materials such as the perovskite SrTiO₃. While traditional BTE methods can qualitatively predict the electron mobility trends in SrTiO₃ up to room temperature, they significantly overestimate the actual values observed in experiments. More advanced perturbative methods that include higher-order electron-phonon interactions show improved accuracy but still fail at elevated temperatures. In contrast, the KG + aiMD approach successfully reproduces experimental mobility measurements across a wide temperature range, maintaining accuracy even up to 900 K.

The implications of this advance may extend far beyond academic interest. Many practical applications, particularly in thermoelectric devices and high-temperature semiconductors, involve materials with strong anharmonic effects. The new method offers possibilities for designing and optimizing such materials. Furthermore, it serves as a valuable benchmark for understanding the limitations of existing perturbative approaches, helping researchers choose the most appropriate computational tools for their specific applications.

A tutorial for the simulation of electronic conductivity and mobility with FHI-aims is available at https://fhi-aims-club.gitlab.io/tutorials/kubo-greenwood-formula.